1. Field of the Invention
The present invention relates to a technical field of a surface-mounting type semiconductor device, and particularly to a technical field of a surface-mounting type semiconductor device having a leadless structure.
2. Background Art
Generally, a semiconductor device includes a metallic lead frame as one component thereof, and micromachining for the pitch of leads in the lead frame is required for forming a greater number of pins therein. However, if attempting to reduce the width of each lead itself, the strength of the lead is lowered, and a short circuit may tend to occur due to bending or the like of the lead. Accordingly, it is unavoidable to upsize the package in order to ensure the pitch of each lead. Thus, a semiconductor device including a lead frame tends to have a package of a greater size and thickness. Therefore, a surface-mounting type semiconductor device having a leadless structure has been proposed.    Patent Document 1: TOKUKAIHEI No. 9-252014, KOHO    Patent Document 2: TOKUKAI No. 2001-210743, KOHO
A semiconductor device described in the Patent Document 1 is shown in FIGS. 11(a) and 11(b). The method of producing the semiconductor device comprises attaching a metal foil onto a base material 101 and etching it such that the metal foil remains at predetermined portions, fixing a semiconductor element 102 onto a metal foil 103a (die pad) having substantially the same size as that of the semiconductor element 102, electrically connecting the semiconductor element 102 and metal foils 103b via wires 105, and transfer molding the connected structure with a sealing resin 106 using a mold. Finally, the molded sealing resin 106 is removed from the base material 101 to form a package of the semiconductor element (FIG. 11b). However, in the semiconductor device formed by this production method, no countermeasure for enhancing the strength of joining each metal foil 103b as a terminal to the sealing resin 106 is provided. Therefore, in the case of further increasing the number of pins of the semiconductor device, downsizing the device and micromachining for the metal foils 103b, the wires tend to disconnect due to peeling of the metal foils 103b. Thus, there is a need for enhancing the strength of joining the metal foils 103b to the resin.
In the method described in the Patent Document 1, sufficient close adhesion between the base material and metal foils is required in the step of etching the metal foil and the molding step using a sealing resin. However, after the molding step, easy separation between the base material and the molding resin and between the base material and the metal foils is also required. As such, the base material and the metal foils are required to have properties which are contrary to each other in the close adhesion property. Namely, while durability to chemicals used for the etching as well as durability that prevents misregistration of the semiconductor element under a high temperature condition in the molding step or under pressure to be applied when the sealing resin flows in the mold are required, after the molding step, easy separation between the base material and the sealing resin and between the base material and the metal foils is required. However, Teflon® materials, silicon materials or metals having Teflon® coatings can not possibly satisfy such a required close adhesion property.
FIGS. 12(a) and 12(b) illustrate a semiconductor device described in the Patent Document 2. Generally, the semiconductor device is produced by the following method. First, a metal plate 201 is obtained by forming square-shaped concave grooves 201a in a metal plate 201 used as a base material. Next, a semiconductor device 202 is fixed onto the metal plate 201 using an adhesive 203, wires 204 are then formed by wire bonding at positions required for a design, thereafter the so formed structure is transfer molded with a sealing resin 205 (FIG. 12(a)). Subsequently, the metal plate 201 and adhesive 203 are grinded together, and the metal plate 201 is cut with the sealing resin 205 in accordance with dimensions conforming to the design so as to obtain a semiconductor device (FIG. 12(b)). However, also in this method, the semiconductor device obtained is not provided with any countermeasure for enhancing the strength of joining the metal plate 201 used as terminals to the sealing resin 205. As in the case of Patent Document 1, with further increase of the number of pins of the semiconductor device and the need of downsizing the device, micromachining of the metal plate 201 should be required. However, when the metal plate 201 is subjected to micromachining, the sealing resin tends to be peeled off. Thus, there is a need for enhancing the strength of joining the sealing resin 205 and the metal plate 201 as well as a need for a multi-pin type small-sized highly reliable semiconductor device.
As described above, in the conventional production methods, for realizing a multi-pin type small-sized semiconductor device, micromachining of electrically conductive portions (terminals) must be required, thus degrading the strength of joining the electrically conductive portions to the sealing resin and making the electrically conductive portions tend to be peeled off from the sealing resin. Therefore, there has been a need for a highly reliable multi-pin type small-sized semiconductor device. In addition, with respect to the need for thinning the semiconductor device, it is required for the conventional methods to grind the semiconductor element (chip) itself into a thinner one so as to obtain a thin type semiconductor device, thus increasing occurrence of breakage or cracks in the semiconductor element during such a production step and hence leading to increase of the cost.